Single gene determines if rare lymphatic system cancer is aggressive

For a rare form of cancer called thymoma, researchers have discovered a single gene defining the difference between a fast-growing tumor requiring aggressive treatment and a slow-growing tumor that does not require extensive therapy.

Thymoma is a cancer derived from the epithelial cells of the thymus, an organ critical to the lymphatic system where T-cells, or so-called killer cells, mature. Very little is known about the role of the gene mutation GTF2l in human tumors, but scientists from Georgetown Lombardi Comprehensive Cancer Center in Washington, DC, and the National Cancer Institute say almost all indolent (slow growing and nonaggressive) forms of thymoma they tested have the mutation. They reported their finding in Nature Genetics (2014; doi:10.1038/ng.3016).

"Indolent thymomas seldom become aggressive, so the discovery that a single gene can identify tumors that do not need aggressive care is an important development for our patients," said the study's senior investigator, Giuseppe Giaccone, MD, PhD, associate director for clinical research at Georgetown Lombardi.

In addition to the clinical implications, the study is important because "it is highly unusual to find a single mutated gene that can define a class of tumors," he said. "Usually a substantial number of genes are involved. In fact, we also found that the more aggressive thymomas express well-known cancer genes found in other tumors, which might give us clues about novel treatment of these cancers."

The thymus is located in the chest behind the breastbone. Thymoma and a second type of cancer of the thymus called thymic carcinoma are rare. According to the National Cancer Institute, these cancers counted together account for only 0.2% to 1.5% of all cancers—one case occurs in approximately every 700,000 persons.

Most of the diagnosed patients have surgery, but, depending on the presumed aggressiveness of the cancer, some patients will have radiation and/or chemotherapy in addition or instead of surgery. "The use of these treatments in thymomas is controversial, because we know some patients don't need aggressive therapy, but until now, there's not been a clear way to know who those patients are," Giaccone said.